Hard disk drives are common information storage devices. FIG. 1a provides an illustration of a typical disk drive unit 100 essentially consisting of a series of rotatable disks 101 mounted on a spindle motor 102, and a Head Stack Assembly (HSA) 130 which is rotatable about an actuator arm axis 105 for accessing data tracks on disks during seeking. The HSA 130 includes at least one drive arm 104 a head gimbal assembly (HGA) 150. Typically, a spindling voice-coil motor (VCM) is provided for controlling the motion of the drive arm 104.
Referring to FIG. 1b, the HGA 150 includes a thermally assisted head slider 103 having a thermally assisted head 110, and a suspension 190 to load or suspend the thermally assisted head slider 103 thereon. The suspension 190 includes a load beam 106, a base plate 108, a hinge 107 and a flexure 109, all of which are assembled together. When the disk drive is on, a spindle motor 102 will rotate the disk 101 at a high speed, and the thermally assisted head slider 103 will fly above the disk 101 due to the air pressure drawn by the rotated disk 101. The thermally assisted head slider 103 moves across the surface of the disk 101 in the radius direction under the control of the VCM. With a different track, the thermally assisted head slider 103 can read data from or write data to the disk 101.
Referring to FIG. 1c, the thermally assisted head 110 has a substrate 1031 with an air bearing surface (ABS) 1032 processed so as to provide an appropriate flying height. The thermally assisted magnetic head 110 includes a write portion 121 having a write element 123 and read portion 122 having a read element. And a thermal energy source 111 is mounted on the substrate 1031 for providing heat energy to the thermally assisted magnetic head 110, such as a laser diode at or near the location of the write portion 121. Conventionally, the thermal energy source is bonded to the substrate 1031 via solders, for example. This thermal energy source provides energy to a portion of the magnetic recording medium, which reduces the medium's coercivity. After that, writing is performed by applying write magnetic field to the heated portion; therefore the writing operation is facilitated. Generally, the thermally assisted magnetic head 110 further includes a waveguide 125 and a plasmon antenna (PA) 127 or a plasmon generator (PG) located near the write element 123. The waveguide 125 is provided for guiding the laser light to the ABS 1032 by a surface of the PG 127, thereby providing near-field light, instead of directly applying the laser light to an element that generate near-field light. Such a PG and a waveguide are disclosed, for example, in US Patent Publication No 2010/0103553 A1 and U.S. Pat. No. 8,059,496 B1.
Conventionally, for preventing the read portion 122 and the write portion 121 from lacking magnetic or being impacted by the external environment, a over coat made by diamond-like carbon (DLC) for example, is covered on the top of all elements mentioned above to form the ABS 1032. However, such a DLC layer couldn't endure the high temperature during the writing operation for the thermally assisted magnetic head slider 103, which may absorb heat significantly and even may be disappeared. Thus the DLC has been replaced with a coat layer 131 with lower extinction coefficient (light absorption index) of complex refraction index made by SiOx, SiNx, SiOxNy, TaOx, TaNx, TaOxNy, hydrogenated amorphous carbon in the thermally assisted magnetic head slider, whose thickness is configured the thicker the better so as to avoid damage happened in the write portion 121 and read portion 122.
However, the thicker coat layer 131 covered on the top surface of the read portion 122 will increase the magnetic spacing between the magnetic recording medium surface and the read portion 122, which will degrade the reading performance of the read portion 122.
Accordingly, it is desired to provide improved thermally assisted magnetic head, HGA, HDD with the same, and a manufacturing method thereof to overcome the above-mentioned drawbacks.